I'd pass on alloying coinage into sterling if I were you. Before
1964, American silver coinage was 90% fine silver, 10% copper. After
1964, the silver content is not even close to 90%. So don't bother
with old coins with their high copper content.
Why not go to your local coin shop and buy 1 ounce fine silver
"rounds" or small bars, and alloy them yourself? Start with your fine
(pure) silver, and order some high-tech alloy for sterling that has
the properties you're looking for, and alloy the sterling yourself in
My students and I love United Precious Metals' S57 NA alloy for
sterling. Far superior to traditional sterling (92.5% fine silver and
7.5% copper), in my opinion.
The math is dead easy: Throw the 1 oz. pure silver round on the
scale, it should be 31.1 gr. With your calculator, divide the weight
of the pure silver (31.1) by.925 ( 92.5%-amount of pure silver in
sterling)and the total comes to 33.6 gr.(sterling silver) Just add
your alloy to the pure silver until your scale reads 33.6, and you
have the correct proportions for your new "high tech" sterling! Easy!